So-called “pop-up” toasters incorporate a toasting chamber with a toasting carriage which can be lowered against a biasing spring for a toasting cycle. A handle is provided for moving the carriage to the toasting position. At the same time as being lowered the toasting carriage makes switch contacts for energising toaster elements and to begin the toasting cycle. The coil of the electromagnet is supplied with current during the toasting operation in order to hold the toasting carriage in a lowered position. At the end of the toasting operation, the supply of current to the electromagnet is stopped, and the toasting carriage rises to “pop-up” the toasted item under the action of the spring.
A prior art toaster of this type has a power circuit that supplies the heating elements with AC power and is operated by a power switch actuated by movement of the toast carriage to the toasting position. Separate from the power circuit, a control circuit to adjust toasting time includes an integrated circuit (IC). Adjustment is accomplished by varying a time constant by means of a manually variable resistor and dependent upon other mode buttons selected by the user (e.g. a “reheat mode” for reduced heating time or a “bagel mode” for extended heating). To improve the reliability of the electromagnet holding action in toasters of this type the applicant designed a toaster described in its Chinese Patent No. 200920003318.X with two DC power supply circuits fed from the mains power. The first DC supply circuit includes a first rectifier connected by a tapping at an intermediate position along the heating element, and includes switches operable for supplying current to operate the electromagnet, and the electromagnet is thus only operable when the heating elements are switched on. The second DC supply circuit supplies current to the control circuit. This second DC supply includes a second rectifier connected to the AC power terminals, such that the control circuit is always live (i.e. has electric potential to electrical ground or neutral) whenever the toaster is plugged into the mains. In the presence of a latching signal from the controller, power supply to the latching electromagnet is maintained. To provide this control signal but isolate the live second DC supply circuit from the heating elements, an optical coupler was used. Although this prior art toaster operates satisfactorily, there is an ongoing need for performance improvements in toasters of this type.
Products containing sugars and fats can, in some situations, catch fire when being toasted. With toasters of the above-described type where the elements are controlled by a timer, independently of the heat load, there is a risk that a fire could be intensified if the heating elements continue to operate while an item to be toasted is burning. There is therefore a need for an improved timer-controlled toaster with anti-burn features which will mitigate the likelihood of a dangerous fire occurring. It is an object of the present invention to overcome or substantially ameliorate the above-mentioned disadvantages or more generally to provide an improved electric toaster.